This'll be very long I apologize in advance.
1. There's a fallacy here in that you're judging things without having tried them akin to "I don't like Sushi", have you tried it? "No, it's disgusting." Another part is that overcoming challenges is fun since it releases endorphins. Much like "I finally got my legendary/skin that you want". The path to it may not be the most fun but reaching your goal is awesome and when you look back it was all worth it.
2. This has little to do with raiding, you're speaking about Q's which you don't have in a raiding guild. There's still RNG but most serious raiding guilds don't use a /roll system on top of the RNG of having your desired item drop, they either use
DKP (an auction like system) or
Loot Council (designated people assign the loot). You only really have to grind if you join late in the season. When WotLK was released many guilds cleared Naxx using T6 gear or simple crafted gear. The idea that you need gear that drops from the raid you're doing is horribly wrong, you can use the gear from previous raid tiers.
3. GW had some raid-like instances: FoW, UW, SF, Deep, Urgoz's Warren, DoA and some missions in Cantha.
4. For the first part, I already addressed this in points 1 and 2, the sub mode again has nothing to do with raiding.
5. Did you like Marrionette/Scarlet fights? Those are a (bad) copy of raids.